The present invention is directed to a method and apparatus for forming a reinforced polymeric container system for pressurized fluids. The method and apparatus advantageously employs coaxial multiple extrusion in conjunction with variable die and vacuum forming capability to form continuous lengths of the container system in an efficient, high-quality manner.
As shown in FIG. 1, U.S. Pat. No. 6,047,860 (the disclosure of which is hereby incorporated by reference) to Sanders, an inventor of the present invention, discloses a container system 10 for pressurized fluids including a plurality of form-retaining, generally ellipsoidal chambers C interconnected by a tubular core T. The tubular core extends through each of the plurality of chambers and is sealingly secured to each chamber. A plurality of longitudinally-spaced apertures A are formed along the length of the tubular core, one such aperture being disposed within each of the interconnected chambers so as to permit infusion of fluid to the interior space of each chamber during filling and effusion of the fluid from the interior space of each chamber during fluid delivery or transfer to another container. The apertures are sized so as to control the rate of evacuation of pressurized fluid from the chambers. Accordingly, a low fluid evacuation rate can be achieved so as to avoid a large and potentially dangerous burst of kinetic energy should one or more of the chambers be punctured (i.e., penetrated by an outside force) or rupture.
The size of the apertures A will depend upon various parameters, such as the volume and viscosity of fluid being contained, the anticipated pressure range, and the desired flow rate. In general, smaller diameters will be selected for gasses as opposed to liquids. Thus, the aperture size may generally vary from about 0.010 to 0.125 inches. Although only a single aperture A is shown in FIG. 1 for each chamber, more than one aperture A can be formed in the tube T within the interior space of the chamber C. In addition, each aperture A can be formed in only one side of the tube T, or the aperture A may extend through the tube T.
The inlet or front end of the tubular core T may be provided with a suitable fitting, such as threaded male fitting 34. The discharge or rear end of a tubular core T may be provided with suitable fitting, such as a threaded female fitting 36. Such male and female fittings provide a pressure-type connection between contiguous strands of assemblies of chambers C interconnected by tubular cores T and provide a mechanism by which other components, such as gauges and valves, can be attached to the interconnected chambers.
The container system 10 is lightweight and robust, and the elongated strand of interconnected chambers can be curved, bent, or otherwise configured to be incorporated into a wearable garment or carryable pack. Examples of such garments and packs are described in U.S. patent application Ser. No. 09/592,902, the disclosure of which is hereby incorporated by reference.
Sanders ""860 discloses an apparatus and method for manufacturing the container system 10 whereby each chamber C includes a discreet, generally ellipsoidal shell molded of a suitable synthetic plastic material and having open front and rear ends. The diameters of the open ends are dimensioned so as to snugly receive the outside diameter of the tubular core T. The tubular core T is attached to the shells so as to form a fluid tight seal therebetween. The tubular core T is preferably bonded to the shells by means of light, thermal, or ultrasonic energy, including techniques such as, ultrasonic welding, radio frequency energy, vulcanization, or other thermal processes capable of achieving seamless circumferential welding. The shells may be bonded to the tubular core T by suitable ultraviolet light-curable adhesives. The exterior of the shells and the increments of tubular core T between such shells are wrapped with suitable pressure resistant reinforcing filaments to resist bursting of the shells and tubular core. A protective synthetic plastic coating is applied to the exterior of the filament wrapped shells and tubular core T.
While the construction described in Sanders ""860 has proven capable of withstanding pressure of the magnitude encountered in portable oxygen delivery systems, e.g., up to 3000 psi, the manufacturing method described in the patent is rather inefficient. The core tube T must be xe2x80x9cthreadedxe2x80x9d through each individual ellipsoidal shell, and each shell must be separately bonded, at each of its longitudinal ends, to the core tube. Accordingly, it is impractical to manufacture strands of interconnected chambers more than several feet long. Moreover, the method requires bond joints at each end of each shell which completely surround the tubular core. These multiple bond joints are subject to manufacturing defects and, regardless of whether the joint includes a defect each bond joint becomes a stress concentration point when the system 10 is pressurized.
As shown in FIG. 2 and described in U.S. patent application Ser. Nos. 09/592,902, 09/592,900, 09/592,904, 09/592,664, 09/592,663, and 09/592,903, the respective disclosures of which are hereby incorporated by reference, the tubular core T can be co-formed along with an outer core 20 having spaced-apart, interconnected shells or chambers 22 and which directly overlies the tubular core. In other embodiments described in the aforementioned patent applications, the tubular core can be omitted, in which case the pressure vessel is comprised of a series of interconnected, hollow chambers.
The present invention is directed to an apparatus and method for co-forming the tubular core T and outer core 20 shown in FIG. 2 in an automated process. The process and apparatus can be expanded to also form the apertures A in the tubular core T, to apply the reinforcement filament layer, and to apply the outer protective layer. In another embodiment of the present invention, the apparatus and method of the present invention can be employed to form a continuous length of interconnected chambers (with the tubular core omitted), which is covered by a reinforcement filament layer and a protective outer coating.
According to a one aspect of the invention, a method for forming a polymeric pressure vessel comprises forming a preform tube with alternating regions of generally uniform wall thickness and internal dimension and regions of increased wall thickness compared to the wall thickness of the regions of generally uniform wall thickness. Each of the regions of increased wall thickness is expanded into a hollow chamber, which has a maximum internal dimension greater than the internal dimension of the regions of generally uniform wall thickness, thereby forming an expanded tube with a plurality of hollow chambers serially interconnected by connecting sections formed by the regions of generally uniform wall thickness and internal dimension.
According to another aspect of the invention, prior to forming the preform tube, an inner tube of generally uniform wall thickness and internal dimension is formed and a plurality of axially-spaced apertures are formed along the length of the inner tube. Thereafter, the preform tube is formed coaxially over the inner tube, with each of the apertures being located within an associated one of the hollow chambers after the regions of increased wall thickness of the preform tube are expanded into hollow chambers.
According to another aspect of the invention, an apparatus for forming a polymeric pressure vessel comprises an outer tube extruder for driving a fluid polymeric material and forming the fluid polymeric material into an outer tubular member. A variable die is located downstream of the outer tube extruder and is constructed and arranged to alternately increase and decrease in size to thereby alternately increase and decrease the thickness of the wall of the outer tubular member. A molding apparatus is located downstream of the variable die and is constructed and arranged to expand spaced-apart portions of the outer tubular member having greater wall thickness into hollow chambers to thereby form a plurality of serially interconnected hollow chambers.
According to another aspect of the invention, the apparatus may also include an inner tube extruder located upstream of the outer tube extruder for driving a fluid polymeric material and forming the fluid polymeric material into inner tubular member and a hole forming device located between the inner tube extruder and the outer tube extruder and constructed and arranged to form axially spaced-apart apertures in the inner tubular member. The outer tube extruder is a coaxial extruder constructed and arranged to form the outer tubular member coaxially over the inner tubular member.
According to another aspect of the invention, the apparatus may include a fusing mechanism located downstream of the outer tube for fusing the outer tubular member to the inner tubular member at locations between the spaced apart hollow chambers.
According to another aspect of the invention, the apparatus may also include a braiding mechanism located downstream of the fusing mechanism for applying a layer of interwoven reinforcing filament fiber over the plurality of interconnected hollow chambers.
According to another aspect of the invention, the apparatus may include an overcoat applicator located downstream of the braiding mechanism for applying a protective layer of polymeric material over the layer of interwoven reinforcing filament fiber.
Other objects, features, and characteristics of the present invention will become apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of the specification, and wherein like reference numerals designate corresponding parts in the various figures.